The present invention relates to an excimer laser device, and particularly relates to an excimer laser device having a cross flow fan for circulating a laser gas.
An excimer laser device using a cross flow fan of which a rotating shaft is supported by magnetic bearings is conventionally known. FIG. 5 and FIG. 6 show an example of an art disclosed in Japanese Patent Laid-open No. 10-173259. FIG. 5 is a sectional side view showing the entire configuration of the excimer laser device, and FIG. 6 is a detailed view of the portion P in FIG. 5. The prior art will be explained below based on FIG. 5 and FIG. 6.
In FIG. 5 and FIG. 6, a laser gas which is a medium for oscillating laser light is sealed in a chamber 2 of the excimer laser device. A cross flow fan 1 provided with a blade section 3 having a plurality of blades and a rotating shaft 9 is disposed in a predetermined position in the chamber 2. The laser gas is circulated by giving driving force to the rotating shaft 9 to rotate the blade section 3, thereby being guided to a space between discharge electrodes 51 and 51. The laser gas is excited by applying a predetermined high voltage across the discharge electrodes 51 and 51, thus oscillating laser light.
The rotating shaft 9 of the cross flow fan 1 is rotatably supported by non-contact magnetic bearings 12 and 12. The magnetic bearings 12 and 12 each include permanent magnets 30, which are annularly mounted on the outer periphery of the rotating shaft 9 and rotate integrally with the rotating shaft 9, and permanent magnets 31 mounted on the inner wall of a casing 14 attached to the outer side of a side wall of the chamber 2. The permanent magnet 31 annularly surrounds the outer periphery of the permanent magnet 30 with a predetermined gap 4 between them. Opposite faces of the permanent magnets 30 and 31 have the same magnetic poles, and the rotating shaft 9 is rotatably supported in a non-contact state by utilizing repulsion between the permanent magnets 30 and 31. In the above configuration, the permanent magnet 30 corresponds to an inner ring section of the magnetic bearing 12, and the permanent magnet 31 corresponds to an outer ring section of the magnetic bearing 12.
A permanent magnet 33 is attached to one end (the right end of FIG. 6) of the rotating shaft 9 of the cross flow fan 1, and faces a permanent magnet 34 across a barrier section 32. The permanent magnet 34 is attached to a motor rotating shaft 37 of a motor 40 attached to the outer wall of the chamber 2, with a magnet supporting body 50 between them. The permanent magnets 33 and 34 compose a magnetic torque coupling 36 for transmitting driving force of the motor 40 to the cross flow fan 1.
The aforesaid excimer laser device disclosed in Japanese Patent Laid-open No. 10-173259, however, has the following disadvantages.
Specifically, since the pressure of the laser gas is high (normally two or more atmospheres) in the excimer laser device, the resistance of the laser gas is large when the cross flow fan 1 rotates in the excimer laser device, thus causing the cross flow fan 1 to vibrate. Imbalance of the weight of the cross flow fan 1 itself also causes vibration. Such vibration extremely increases, for example, when the cross flow fan 1 resonates or the blade section 3 twists.
However, according to the aforesaid prior art, no means for suppressing the vibration and protecting the magnetic bearing 12 against breakage when the cross flow fan 1 vibrates is provided. Thus, there arises a disadvantage that force larger than the repulsion between the permanent magnets 30 and 31 of the magnetic bearing 12 is applied to the magnetic bearing 12, thus causing the permanent magnet 30 and the permanent magnet 31 to collide with each other to thereby break the magnetic bearing 12.
The vibration of the cross flow fan 1 is further increased by such breakage, thus sometimes causing the optical axis of the excimer laser device to deviate, and moreover causing the cross flow fan 1 to come off the magnetic bearing 12 to thereby collide with components such as discharge electrodes and the like. In the above case, it is required to stop the excimer laser device and replace the magnetic bearing 12, which causes a disadvantage that this work takes a great deal of time, labor, and cost.
The present invention is made in view of the aforesaid disadvantages, and its object is to provide an excimer laser device having the functions of suppressing vibration of a cross flow fan, and preventing breakage of magnetic bearings when the vibration increases in spite of the above suppression.
A first configuration of an excimer laser device according to the present invention is characterized in that an excimer laser device having magnetic bearings each having an inner ring section mounted on the outer periphery of a rotating shaft and an outer ring section supported by a chamber, and a cross flow fan rotatably supported in a non-contact state in the chamber by the magnetic bearings via the rotating shaft and circulating a laser gas in the chamber, includes
touch-down bearings on the outer peripheral side of the rotating shaft, and that
the inner peripheral face of an inner peripheral portion of the touch-down bearing and the outer peripheral face of the rotating shaft are disposed opposite each other with a predetermined clearance smaller than a gap between the outer peripheral face of the inner ring section and the inner peripheral face of the outer ring section.
According to the above configuration, the touch-down bearing is disposed on the outer peripheral portion of the rotating shaft with a predetermined clearance between them. Therefore, when the rotating shaft vibrates, the rotating shaft collides with the touch-down bearing before the inner ring section of the magnetic bearing collides with the outer ring section thereof. Thus, the inner ring section and the outer ring section of the magnetic bearing do not collide with each other, thereby preventing the breakage of the magnetic bearing. Consequently, the rate of operation of the excimer laser device is improved.
A second configuration of an excimer laser device according to the present invention is characterized in that an excimer laser device having magnetic bearings each having an inner ring section mounted on the outer periphery of a rotating shaft and an outer ring section supported by a chamber, and a cross flow fan rotatably supported in a non-contact state in the chamber by the magnetic bearings via the rotating shaft and circulating a laser gas in the chamber, includes
gap measuring means each for measuring a value of a gap between the outer peripheral face of the inner ring section and the inner peripheral face of the outer ring section, and
gap controlling means each for controlling the value of the gap within a predetermined range based on signal output from the gap measuring means.
According to the above configuration, the gap measuring means for measuring the gap and the gap controlling means for controlling the gap are provided, which makes it possible to control the gap to suppress the vibration of the rotating shaft, thereby reducing vibration of the cross flow fan. As a result, the optical axes of optical elements of the excimer laser device scarcely deviate, thereby stabilizing the characteristic of laser light. Moreover, the breakage of the magnetic bearing is prevented, thus improving the rate of operation of the excimer laser device.
A third configuration of an excimer laser device according to the present invention is characterized in that an excimer laser device having magnetic bearings each having an inner ring section mounted on the outer periphery of a rotating shaft and an outer ring section supported by a chamber, and a cross flow fan rotatably supported in a non-contact state in the chamber by the magnetic bearings via the rotating shaft and circulating a laser gas in the chamber, includes
gap measuring means each for measuring a value of a gap between the outer peripheral face of the inner ring section and the inner peripheral face of the outer ring section, and that
laser oscillation is stopped and rotation of a motor for driving the rotating shaft is stopped when the measured value is smaller than a predetermined value.
According to the above configuration, when abnormal vibration occurs, the rotation of the motor is stopped. As a result, the cross flow fan never rotates in the state of abnormal vibration, thereby preventing the breakage of components such as the cross flow fan and the like. Hence, the rate of operation of the excimer laser device is improved.